1. Field of the Invention
Proportioning devices for vehicle hydraulic brake systems.
2. Description of the Prior Art
In conventional proportioning valves for hydraulic vehicular brake systems, the effect of weight transferred from the rear wheels to the front wheels during a braking operation is compensated such that upon attainment of a selected level of output pressure from the master cylinder of the associated brake system, further pressure increases to the rear brakes occur at a preselected ratio, resulting in the brake pressure applied to the rear brake system being predeterminately less than the master cylinder pressure. The purpose of this, of course, is to deter premature lockup of the rear wheels during braking as the weight is transferred from the rear wheels to the front wheels of the associated vehicle.
Although proportioning valves heretofore known and used in the prior art have been capable of closely approximately the idealized relationship between the pressure to the front brakes (often the master cylinder) and the pressure to the rear brakes, under various loading conditions, there can be substantial deviation between the idealized relationship and the actual performance of the proportioning valves. The problem of modifying the operation of proportioning valves in accordance with the vehicle loading has been approached in a number of different ways, primarily through the use of various connections or linkages between the proportioning valves and the associated vehicle suspensions; however, such arrangements have been objectionable due to the space requirements for the connecting elements and the expense involved in manufacturing, installing and maintaining the same.
The invention disclosed in the U.S. Pat. No. 3,881,786 and assigned to the assignee of the present application, overcomes a number of the objectionable characteristics of load sensitive proportioning valves which sensed suspension loading of the associated vehicle, and the present invention is related to and consists of an improvement over the valve assembly shown in the aforementioned application.